(1) Field of the Invention
The present invention relates to disposable air filters, and is more particularly concerned with an air filter which is compact and which may be inexpensively fabricated of readily available materials.
(2) Prior Art
Fibrous glass air filter units have met outstanding commercial success for a long period of time. Such filters are constructed of a filter element formed of glass fibers coated with a sticky substance for holding particles impinging against the fibers in adherence thereto. Because of their high efficiency, reasonable cost, and inertness to corrosive agents, such filters rapidly have established an important position in domestic forced air heating and air conditioning installations. This success has been attributed to the attractive, simple and economical form in which the units have been produced as well as to the excellent and aggressive sales promotion of the products.
The design of the air filter has remained substantially unchanged since its early introduction. Such structure comprises the filter element formed of a core of glass fibers bound together by small particles of a resinous binder and coated with a thin transparent film of a viscous non-volatile oil, to retain airborne particles impelled against the fibers by the air movement. The filter element is retained between two closely perforated sheets of tin plate metal commonly known and available as bottle cap scrap. The filter and the pair of perforated confining tin plate sheets are held together within an inwardly facing U-channel of a hollow frame of sturdy but inexpensive fiberboard, often decorated and reinforced by an overlay of imprinted paper tape. The structure may be held together with a hot melt adhesive or with staples and a tape with adhesive back.
The bottle cap scrap is a unique adjunct of these air filters and appears in part to account for a portion of the commercial success and sales appeal of the product. The scrap is perforated stock obtained from bottle cap plants where the stock is punched with circular orifices placed as closely together as possible, the area of the circular orifices thereby accounting for nearly 90% of the total area of the stock. With the advent of newer caps for the bottling industry, such as screw-on caps formed of aluminum, and with the advent of container cans for beverages, bottle cap scrap is becoming scarce and is at a premium.
Air filter units have been characterized over the years in being virtually unchanged in their shape and structure. The air filter units are generally in a rectangular form commonly available in thicknesses of 1/2 to 2 inches, and with varying dimensions to provide filtering areas between 1/2 and 4 square feet. Because of the inwardly facing U-channel frame of the filtering unit, it is not compact nor can it be compressed or nested in packaging, and thus poses a serious bulk problem. Even though the packaged units may be lightweight, such lightweight bulky packages pose a serious problem where shipping costs are based on volume as well as weight.
Recently, more compact units have appeared as shown in U.S. Pat. Nos. 2,965,197; 3,467,257; and 3,023,839. However, such units have not been entirely satisfactory because of extra strength reinforcement requirements necessitated by the elimination of the bottle cap scrap facing entirely. The need for complex or exotic structural reinforcement arrangements has mitigated against acceptance of these filter units by both the air filter units manufacturer and the consuming public. In addition, as to the consumer, these units just do not have the appeal of the air filter unit with which the consumer is familiar. In U.S. Pat. No. 3,830,045 an improved air filter is disclosed and claimed wherein the frame of the filter is so designed that a plurality of filters may be nested within one another. Moreover, the filter is so designed that only a single bottle cap scrap sheet need be used. However, it would be desirable to dispense entirely with the need for bottle cap scrap as a backing cover for a filter. Moreover, the frame of the structure in question is formed of a plurality of frame members which must be glued together to form the entire frame, and the strength and rigidity of the frame structure should desirably be greater.